1. Field of the Invention
The present invention relates to high pressure gate valves. The present invention more particularly relates to high pressure gate valves for use with for example, oil or gas well completion operations.
2. General Background and Prior Art
In the completion of testing oil and gas wells, there is a significant danger of the escape of oil and/or gas from the well structure before the well is finally completed and piping set up. During this time, it is necessary that the well be properly valved at the well opening. Such a completion valve must handle high pressures such as, for example, 15,000-20,000 p.s.i.
Many times a well is provided with a blow-out preventor (b.o.p.), also referred to as a "b.o.p." stack. The blow-out preventor or "b.o.p." stack is used on the well and is provided with closures which are called rams, which when activated can shut off the well in the event of a blow-out. The rams have sufficient strength to shear pipe, or other material which is in the well bore. Thus, the placement of equipment in the blow-out preventor stack does not negate the chance for closure. However, it would be desirable to have the safety factor of a primary valving system which would attach to the wellhead, yet be small enough to fit into the "b.o.p." stack and still be able to withstand, for example, 15,000-20,000 p.s.i. pressures as can be generated by the well at the wellhead.
In offshore well completion, a ship, or other mobile type drilling rig is employed usually in offshore well completion. In severe weather, the ship may be forced to break its connection with the well and return at a later time when seas have calmed. There is a need at this time for a valve structure preferably automatically when the ship either purposely or by accident breaks its connection with the oil well. It would be preferable that such a valve would fit inside the standard convention b.o.p. stack or blow-out preventors now on the market.
Valves which have attempted to solve the problem of offshore well completion, or sub surface use are generally faced with a size and pressure problem. Valves which are strong enough to withstand high pressures, must be manufactured generally of a size and configuration as to be unsuitable for placement within a b.o.p. stack or within casing.
Ball valves have been used, but have been less than satisfactory because of a warping problem with the valve when subjected to high pressures. The ball portion of the valve becomes somewhat "egg" shaped when subjected to high pressures, as the intense pressure tries to flatten the ball, thus producing the egg shape or lopsided warping of the valve ball portion. It will be appreciated that such warping removes the capacity of a valve to properly operate since it will no longer seat in a true fashion within the valve body.
Gate valves would be more suitable for a high pressure environment, but gate valves generally require a large configuration with the gate member of the valve (i.e. the actual valving member) projecting a distance laterally beyond the body of the valve. Such a configuration is unsuitable for placement in confined cylindrical or like openings such as within the casing or b.o.p. stack of an oil or gas well. Indeed, some casing and b.o.p. stack structures have dimensional openings on the order of 131/2 to 14 inches in diameter. It would be desirable to have a gate valve which could fit within such a 131/2 inch to 14 inch diameter, yet provide a desirable gate valve to combat the warping problem of ball valves, yet still be structurally sound to produce working pressures on the order of 15,000 p.s.i. Still another requirement of such a valve would be to provide a bore of constant cylindrical shape having a two inch or three inch opening (while still maintaining the minimum overall body diameter of 135/8 inches, for example), the valve bore allowing wire line tools and conductor line tools to be run down the well hole and through the valve bore. It would also be desirable to have a gate valve type valving member to produce a shear which could cut wire lines or conductor lines in the event that it would be desirable to close the valve quickly before the wire line or conductor lines could be removed. Such a shearing would be available with a powered gate valve construction.
Valves for use in such an environment should have a simple construction, with preferably interchangeability of parts as much as possible.
Often, it is necessary to operate a valve from within the valve bore or from outside the valve body where the valve operative source (such as hydraulic pressure) has been lost. This would be referred to as "annular" sensitive (outside operation) and "surface" sensitive (inside operation). It would be desirable that the valve could be operated by injecting pressure into the valve bore in order to open the valve when it is closed. In a like manner, it would be desirable to inject pressure about the outside body portion of the valve and allow it to be opened when closed and when normal connections to the valve are inoperative.